The results of a new single-center study indicate that tetanus, diphtheria, and acellular pertussis (Tdap) immunization during the third trimester of pregnancy was associated with higher neonatal concentrations of pertussis toxin antibodies when compared with no immunization.

The results of a new single-center study indicate that tetanus, diphtheria, and acellular pertussis (Tdap) immunization during the third trimester of pregnancy was associated with higher neonatal concentrations of pertussis toxin antibodies when compared with no immunization. Concentrations were highest when Tdap immunization occurred at 27–30 weeks, researchers report. The prospective cohort study of 626 pregnancies in Houston found that neonates whose mothers received Tdap immunization during weeks 27–36 of pregnancy had a geometric mean concentration of pertussis toxin antibodies in their cord blood of 47.3 IU/mL, compared with 12.9 IU/mL for neonates whose mothers did not receive the Tdap vaccine during pregnancy. "This study is the first, to our knowledge, to evaluate a large cohort of newborn infants born at term to mothers who received Tdap vaccine in accordance with the current U.S. recommendations," the researchers conclude. "These serologic findings may help to explain why epidemiologic studies demonstrated reduction in infant pertussis following third-trimester immunization in the United States and in the United Kingdom, where pertussis booster vaccine was given during weeks 28 to 38 of pregnancy and resulted in a 91% reduction in pertussis in infants 3 months or younger."